Endogenous fluctuations in the brain were evaluated by simultaneously measuring
electrophysiological and fMRI signals in the awake monkey. Fluctuations of the
gamma local field potential power and fMRI signals were strongly correlated,
not just in the region of the electrode but across a large portion of the
cerebral cortex, an effect that was strengthened when the monkeys eyes were
closed. These findings demonstrate that a significant portion of the variance
in resting state activity is correlated with underlying neural activity, and
that the relationship between fMRI and neural signals varies as a function of
behavioral state.